Targeted microRNA characterization in various brain cell‐derived exosome subtypes to identify novel biomarkers for Alzheimer’s disease

Abstract

AbstractBackgroundMicroRNAs (miRs) offer exciting diagnostic and therapeutic opportunities for Alzheimer’s disease (AD). However, most information about human miRs is from either plasma or CSF of uncertain cellular origin or from postmortem AD brain, which suffers significantly for miR integrity and expression. The discovery of brain cells‐derived exosome (BCDEs) in plasma has led to studies examining their role as ‘liquid biopsies’ for AD. Here, we simultaneously isolated 6 BCDE subtypes from plasma and characterized them for specific miRNAs regulating synaptic plasticity, memory, Aβ, tau, ischemia, and neuroinflammation related signaling pathways.MethodTE were isolated from plasma samples obtained from the Wake Forest Alzheimer’s Disease Research Center: normal cognition (NC; n=8), mild‐cognitive impairment (MCI; n=3), MCI to AD (n=6), and AD (n=11). Next, following 6 BCDE subtypes were extracted using streptavidin‐coated magnetic beads and specific biotin‐tagged antibodies: neuron‐derived exosomes (L1CAM‐biotin antibody), astrocytes‐derived exosomes (GLAST‐biotin antibody), microglia‐derived exosome (TMEM119‐biotin antibody), oligodendrocyte‐derived exosomes (PDGFRα‐biotin antibody), endothelial‐derived exosomes (PECAM1‐biotin antibody), and pericyte‐derived exosomes (PDGFRβ‐biotin antibody). The purity, concentration and size of TE and each BCDE subtype was assessed by flow cytometry, nanoparticle tracking, immunogold labeling, and electron microscopy. The expression of 8 specific miRs (miR‐9a‐5p, miR‐29‐5p, miR‐106‐5p, miR‐107, miR‐125b‐5p, miR‐132‐5p, miR‐135b‐5p, and miR‐210) was measured by TaqMan assays on real‐time PCR.ResultWe observed statistically significant changes in the expression of all 8 miRs in various BCDE subtypes at MCI, MCI‐AD and AD stages. Importantly, we did not observe significant change for most miRNAs in TE, except for miR‐107 and miR‐135b‐5p, highlighting the importance of studying BCDE. Moreover, basal expression of several miRNAs was significantly different between TE and BCDEs. Interestingly, miR‐106b‐5p, miR‐135b‐5p, miR‐107, and miR‐9a‐5b consistently showed significantly higher expression at MCI, MCI‐AD and AD stages for most BCDE subtypes. While the expression of miR‐125b‐5p, miR‐29a‐5p, and miR‐132‐5p showed statistically significant differences based upon BCDE subtype (either an increase or a decrease); for hypoxiamir ‘miR‐210’, expression was higher at MCI stage but decreased with AD progression.ConclusionBCDEs characterization in plasma offers a less invasive opportunity to better understand AD pathogenesis at the cellular level, and to discover novel theranostic targets.